DRM_MM_INSERT_ONCE
once = mode & DRM_MM_INSERT_ONCE;
mode &= ~DRM_MM_INSERT_ONCE;
if (mode & DRM_MM_INSERT_ONCE) {
DRM_MM_INSERT_HIGHEST = DRM_MM_INSERT_HIGH | DRM_MM_INSERT_ONCE,
DRM_MM_INSERT_LOWEST = DRM_MM_INSERT_LOW | DRM_MM_INSERT_ONCE,